This project is designed to apply multidisciplined capabilities to study the intimate relationship between blood perfusion dynamics and solute exchange in the microcirculation. Preparations of living perfused tissue are studied on specially designed intravital microscopes. Microscopic observation is arranged to encompass registration of the entire pattern of distribution of the microvessels and to record flow through each vessel in sufficient detail to analyze flow dynamics (particularly velocity and diameter) in the interconnected mesh. Hydrophilic solute transport is detected in spatial relationship to the individual exchange vessels. Small uncharged molecules and ions are detected by radionuclide labels in a spatially discriminate system. Macromolecules are detected by fluorescent emissions from demonstrably stable tagged sites. Each study defines the spatial-temporal movement of tracer from vessel to interstitium or interstitium to lumen. Data can then be processed to evaluate (1) kinetics of transport across vascular walls, (2) kinetics and routes of transport through interstitium, for a variety of molecular species. Precise localization can be enhanced by correlated ultrastructural studies. In final form the results are expected to improve quantification of the processes of vascular-tissue exchange in relation to specific vessels under known flow conditions.